Significant volumes of oil are known to exist in permeability-contrast subterranean reservoirs that include one or more high permeability regions adjacent to and/or in fluid communication with one or more low permeability, but porous, regions. A significant percentage of the oil in place in such reservoirs may be contained within the low permeability regions. Primary and secondary oil recovery techniques may be effective at removing the recoverable oil from the high permeability regions of the reservoir; however, it may be difficult to remove the oil contained within the low permeability regions of the reservoir without improvements to standard oil recovery techniques.
Examples of secondary oil recovery techniques that may be utilized to enhance the recovery of oil from subterranean reservoirs include fluid injection techniques such as waterflooding and steam flooding, which respectively include the injection of liquid water and steam into the reservoir to mobilize and sweep fluids from the reservoir and the production of the mobilized and swept reservoir fluids from the subsurface formation containing the subterranean reservoir. However, since pressurized fluids tend to flow along the path of least resistance, the presence of a high permeability region in fluid communication with a low permeability region, as is the case within high permeability-contrast subterranean reservoirs, may result in channeling of the injected and/or the produced fluids through the high permeability region. While this may enable efficient sweep of the high permeability region of the subterranean reservoir, a significant percentage of the oil present within the low permeability region may remain despite the employment of these secondary production techniques.
One method of increasing oil recovery in high permeability-contrast subterranean reservoirs may be through tight well spacing, such as through drilling additional injection and/or production wells within the subterranean reservoir, and especially in the low permeability region thereof. This approach may increase the percentage of oil that may be removed from the subterranean reservoir over a reasonable time frame. However, the increased costs associated with drilling additional wells may be prohibitive. In addition, unless the distance between the wells is relatively small, a significant percentage of the potentially recoverable oil may still remain within the low permeability region. Thus, there exists a need for alternative methods to improve the recovery of oil from high permeability-contrast subterranean reservoirs.
Traditional waterflooding techniques have been modified in a variety of ways to improve oil recovery from high permeability-contrast subterranean reservoirs. One such modification is to decrease the permeability of the high permeability region and thus reduce the driving force for channeling by artificially creating a more uniform overall permeability within the subterranean reservoir. This may be accomplished by providing a blocking agent that is adapted to partially and/or completely occlude the pore structure of the high permeability region of the subterranean reservoir. This occlusion may be accomplished by supplying an intact blocking agent to the high permeability region and/or by forming the blocking agent in situ, generally in the vicinity of a well. Illustrative, non-exclusive examples of intact blocking agents that may be supplied to the subterranean reservoir are disclosed in U.S. Pat. Nos. 3,323,589, 4,182,417, and 6,228,812, the complete disclosures of which are hereby incorporated by reference. Illustrative, non-exclusive examples of blocking agents that may be formed in situ are disclosed in U.S. Pat. Nos. 3,530,937, 4,098,337, 4,361,186, 4,637,467, 4,643,255, and 7,021,376, the complete disclosures of which are hereby incorporated by reference. While these approaches may be effective under certain conditions, changing the bulk permeability of the high permeability region may require that a large mass of blocking agent be supplied to the subterranean reservoir. Moreover, optimally placing the blocking agents may be difficult if the high permeability region covers a large area or is not immediately adjacent to a well.
An alternative approach may be the formation of a hydraulic barrier. While the use of near-wellbore hydraulic barriers to decrease water and/or gas coning is disclosed in U.S. Pat. Nos. 3,297,088, 3,369,605, 5,067,564, 5,259,453, and 5,476,145, the complete disclosures of which are hereby incorporated by reference, these barriers are constrained to within a few meters of the wellbore, may rely on manmade horizontal fractures for their formation, and are not formed at an interface between high and low permeability regions of the subterranean reservoir.